<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .wrap{
            width: 1000px;
            height: 500px;
            background-color: #e8e8e8;
            margin: 0 auto;
            display: flex;
            justify-content: space-around;
            align-items: center;
            flex-wrap: wrap;
        }
        .child{
            width: 300px;
            height: 300px;
            border: 2px solid black;
            background-color: #CCCCCC;

        }
    </style>
</head>
<body>
    <div class="wrap">
        <div class="child">1</div>
        <div class="child">2</div>
        <div class="child">3</div>
        <div class="child">4</div>
        <div class="child">5</div>
        <div class="child">6</div>
    </div>
</body>
</html>
